Field of the Invention and Description of the Prior Art
This invention relates to an improved mechanism for controlling the direction of flow of concrete from the outlet of a concrete mixing drum, and it particularly relates to a mechanism for controlling the direction of flow of concrete from a front discharging type of concrete mixer mounted on a truck chassis.
It is very common today to mount a concrete mixing drum on the chassis of a truck in order that concrete can be mixed enroute from the place of loading or charging of the mixer to the place were the concrete is to be poured. The advantages of mounting the concrete mixing drum on a truck chassis are well known and are primarily significant savings in the production of concrete and in speeding up construction time as the vehicles can be brought close to the place where the concrete is to be poured.
The most common practice for years was to mount the concrete mixer in such a way as the discharge was directed rearwardly of the vehicle. In this case, one person would manually position the discharge end of a discharge to the position where the concrete was to be poured while the truck driver manipulated the vehicle to the desired position. Thus, with rear discharge mixers, the pouring of concrete from the mixer was a two man job. In order to economize on labor, in more recent years, it has become the practice to mount the discharge opening and chute at the forward end of the vehicle so that the driver alone can generally view and control the direction of flow of concrete when seated within the cab of the truck.
One such patent which shows a front end discharging arrangement is Hansen et al. U.S. Pat. No. 3,334,872. In this patent, the discharge chute is rotatably moved about a substantially upright axis by the use of a rather complex arrangement of a double-acting, double-ended power cylinder operating in combination with cables and pulleys for imparting the desired rotational movement to the discharge chute. The actual movement is accomplished by a frictional engagement of the carriage assembly for the chute with the cable, which is moved by the cylinder. This arrangement is not only a relatively complex construction, the friction drive is not always completely reliable. For example, when a truck is not parked on level ground, and the chute must be pivoted or swung in an uphill direction, the friction drive mechanism sometimes does not have adequate drive power to pivot the chute assembly. Also, concrete, particularly that which hardens on the operating parts, as the piston rod, can adversely affect the operation of the mechanism.
In another known system, a chain drive is used in combination with a hydraulic motor to engage a sprocket in an assembly which rotatably moves the chute assembly about an upright axis. The chain drive is considered unsatisfactory because, during use, the chain often stretches, becomes disengaged from the sprockets and actually may fall from the equipment. Another disadvantage is that as concrete hardens and builds up on the chain, it ultimately breaks.
In another known mechanism for rotating a discharge chute of a front discharge mixer, a hydraulic cylinder operates a crank which, in turn, operates a gear segment which engages a drive gear segment for rotating the chute assembly. Such an arrangement, however, is considered unsatisfactory because, as mentioned above, concrete builds up on the cylinder rod and adversely affects operation.
Thus, although various mechanisms have been used for rotating the discharge chute for a concrete mixer about an upright axis, particularly of the type used in a front discharge type of a concrete mixer truck, it is apparent that there is a significant need for a more reliable mechanism for controlling the flow of concrete wherein the mechanism is simpler in construction and more reliable in use.